Centrifugal compressor



Dec. 28, 1965 A. TRASK 3,226,012

CENTRIFUGAL COMPRESSOR Filed Oct. 28, 1963 i INVENTOR.

ALLEN TRASK 2 3 W 25 ATTORNEY United States Patent 3,226,012 CENTRIFUGAL COMPRESSOR Allen Trask, 1 Noyes St., Utica, N.Y. Filed Oct. 28, 1963, Ser. No. 319,325 4 Claims. (Cl. 230117) This invention relates to gaseous fluid compressors, and more particularly to centrifugal compressors comprising a rotor wherein compression is effected by centrifugal force acting on a fluid as it flows through passages in the rotor between its central part and its periphery.

Centrifugal compressors have important advantages in mechanical simplicity, quietness of operation, long life and high efliciency. The centrifugal compressors of current design have the disadvantages of being limited to large size and high peripheral speeds of the rotors.

A principal object of this invention is to provide a centrifugal compressor basic design for gaseous fluids which is efficient in comparatively small sizes operating at the r.p.m. of standard two pole induction motors.

Another object of the invention is to provide a structural design adapted to quantity production of small compressor sizes at low cost.

A further object of the invention is to provide at hermetic type compressor adapted to the common refrigerants for use in refrigeration and air conditioning systems in the range of ten tons capacity and smaller, as well as in larger sizes.

Still another object of the invention is to provide a basic structural design adapted to a choice of different compression ratios using the same rotor diameter and r.p.m.

Another object of the invention is to provide a centrifugal compressor in which the flow of gaseous fluid through radial passages in its rotor is so controlled that the action of centrifugal force thereon will effect compression of the fluid in proportion to the increase in centrifugal force in effect between the inlet and the outlet of the passages.

Still another object of the invention is to provide a structural design adapted to both high and low intake pressures thus making the compressor suitable for use in multiple stage compression designs for reaching high pressures.

A centrifugal compressor embodying this invention may have the gaseous fluid to be compressed enter the central chamber of its rotor through the rotor shaft. A number of narrow radial passages provide open communication between a central chamber in the rotor and its periphery. These passages are uniformly tapered with the widest end open to the central chamber in the rotor, and the smallest end open to the periphery of the rotor. The cross section area of each passage decreases radially outward substantially in inverse proportion to the increase of centrifugal force acting on a fluid being compressed as it flows radially outward through each passage.

As a column of fluid in each radial passage moves radially outward it flows in substantial equilibrium established by a progressive and continuous balance between radially increasing centrifugal force, friction resistance to fluid flow and proportionately increasing fluid pressure caused by the progressive reduction of cross se'ctional area of the passage which progressively converts increasing centrifugal force into increased fluid pressure. Since the fluid flows in equilibrium, it flows at a substantially constant velocity impel-led by the substantially constant amount of centrifugal force used to overcome fluid friction against the walls of the passage.

Thus the amount of compression accomplished is in 3,226,012 Patented Dec. 28, 1965 proportion to the increase of centrifugal force at a passage outlet over the centrifugal force in effect at its inlet opening. When a compressor rotor constructed in accordance with this invention has its radial passages designed with the required configuration and is rotated at the required speed the compression ratio available is substantially proportional to the ratio of the area of a radial passage inlet opening to the area of its outlet opening.

The foregoing brief outline of some of the principal objects and advantages of this invention, and the novel structural features of a centrifugal compressor by which they may be accomplished, will be more readily understood in the following detailed description wherein reference is made to the accompanying drawings:

FIG. 1 is a vertical sectional view through a centrifugal compressor embodying this invention adapted to being driven through its shaft extension by external power means;

FIG. 2 is a plan view of a compressor rotor disc sandwiched between two other rotor discs;

FIG. 3 is a side view of the rotor discs shown in FIG. 2;

FIG. 4 is a diagram indicating the structural relationship and proportions involved in the designing of a tapered slot in a rotor disc of the present invention; and

FIG. 5 is a vertical sectional view through a centrifugal compressor of the hermetic type wherein an electric motor for driving it is enclosed in a common housing with the compressor rotor.

Referring first to FIG. 1, a compressor housing 1, is assembled into a fluid pressure tight compression chamber 2, by means of bolts 3, and gasket 33. The compressor shaft 4, is journaled in bearing 5, shown on the right hand end of housing 1, and in ball bearing 6, at the opposite end of the shaft in the left hand end of housing 1. A shaft seal ring 7, in seal chamber 19, is held in contact with seal plate 8, by spring 9, to effect a fluid tight seal at the point where shaft 4 extends through housing 1 to the outside where it may be connected to a power means not shown, for driving the compressor.

The rotor assembly includes a number of concentric annular discs 10, separated alternately by one annular disc 11 of smaller diameter between each two discs 10. The discs may be punched from flat sheet metal and coated with a gasket material for effecting a fluid tight seal between them. The discs may be stamped out of metal strip stock on automatic punch presses in the manner electric motor rotor laminations are produced. The discs 10 and 11 are held concentrically tight together between rotor end plates 12, by means of bolts 13. A central chamber 14 in the rotor is defined by the inside diameters of the plurality of annular discs 19 and 11, and the rotor end plates 12. The hub 34 of each rotor end plate 12, fits shaft 4, and the fit is made fluid tight by an O ring 15 in each hub. The assembled rotor is secured to shaft 4, by means of shaft nut 16, at the left hand end of the shaft exerting pressure against the inner race of ball bearing 6, through hubs 34, and the split retaining washer 17.

Shaft 4 is a hollow and closed at both ends. It is drilled from the left hand end as far as seal ring 7, and is closed at the left hand end with plug 18. The gaseous fluid to be compressed enters seal chamber 19, through opening 20 in housing 1. it flows into hollow shaft 4, through the shaft openings 21. Openings 22 in shaft 4, provide fluid communication from the inside of the shaft to the rotor central chamber 14. Fluid passages through the rotor discs 10, and 11, are shown in FIG. 2 and FIG. 3, and are explained hereinafter.

A lubricant reservoir 27, is shown in this embodiment of the invention separate from the compressor housing From the seal chamber 19,

1. A conduit 28 extends from the lower portion of reservoir 27, to the portion of housing 1, surrounding bearing 5, where it is in communication with shaft 4, and bearing 5, through drilled passages 29. A conduit 30 provides communication for lubricant from the lower portion of housing 1, to reservoir 27. A pressure balancing conduit 31, communicating between housing 1, and reservoir 27, and located above conduit 30, provides means for maintaining equal fluid pressure within housing 1, and lubricant reservoir 27.

FIGS. 2 and 3 illustrate the manner in which one annular disc is sandwiched between two annular discs 11, of smaller diameter. In such a fashion the rotor assembly of a number of discs 10 are separated from each other by discs 11, where they are stacked between rotor end plates 12, and are firmly held together by bolts 13. The larger diameter disc 10 is shown with sixteen (16) tapered radial openings or solts 23, spaced symmetrically around the disc. Bolt holes 24 are spaced symmetrically, but unevenly between respective openings 23, for receiving bolts 13, which hold the discs and rotor end plates 12 in concentric assembly. When discs 10 are alternately reversed in assembly, the outward end openings 26 of tapered openings 23, are out of alignment and not opposite each other in adjacent discs.

Referring again to FIG. 2, the radial tapered openings or slots 23, in the discs 10, become radial tapered open passages when closed on both sides by discs 11. The tapered passages extend radially inward with their inside ends 25 extending beyond the inside diameter of annular discs 11, to provide communication for fluid from the rotor central chamber 14, flowing between the inside portions of annular discs 10, to enter tapered passages 23. Tapered passages 23 extend radially outward with their outward ends 26 extending beyond the outside diameter of annular discs 11, to provide communication for fluid to flow from the tapered passages 23, between the outward portions of discs 10, and into the compression chamber 2, inside housing 1. Housing 1 has outlet opening 32 for the fluid which has been compressed. Thus the fluid being compressed is free to flow from the central rotor chamber 14, radially out- Ward through open tapered passages 23, into compression chamber 2, and out compressor discharge opening 32.

The tapered passages 23 in the discs 10 may be stamped on punch presses and stacked in the numbers required for assembling rotors having different compression capacities in the volume of fluid compressed. Rotors may be assembled using discs of any thickness suitable to the overall compressor design and the fluid to be compressed, or they may be constructed With tapered passages in a single plane in one piece of material such as a die casting or moulded plastic. While the passages are shown to be radial in the preferred embodiment of the invention, they may be arranged to slant either forward or backward from a radius in the manner of the blade arrangements of centrifugal blower wheels having blades sloping either forward or backward to better meet the application for which they are designed. In like manner passages 23 may be forwardly curved or backwardly curved in the manner of conventional blade design of centrifugal blowers, to better meet the requirements of the overall compressor design.

FIG. 4 shows a diagram of one of the tapered passages 23, which may be used as help in calculating the dimensions of and the radial location of the tapered passages of a centrifugal compressor rotor embodying this invention.

If the density of the fluid to be compressed would remain constant during the process of compression then centrifugal forces acting on the fluid during its flow through a passage would increase as the square of the radii from the rotor center, and the passage taper required to counterbalance the centrifugal force would diminish radially outward substantially in inverse proportion to the square of the radii from the center of L=length of a tapered passage 23 R =radius at the inlet of the tapered passage W =width of the tapered passage at its outlet W =width of the tapered passage at its inlet.

However, during the process of compressing a gaseous fluid the density of the fluid will be increased in proportion to the increase of pressure to which it is subjected. Under isothermal compression the weight of the fluid per unit volume would for instance be doubled under a compression ratio of two to one which woud double the pressure on the fluid. Thus it may be considered that the centrifugal force acting on the fluid during its :flow through a passage would increase substantially as the third power or the cube of the radii from the rotor center. Thus the taper of the passage required to counterbalance the full effect of the centrifugal force acting on the fluid will be substantially in inverse proportion to the cube of its radii from the rotor center. Under this analysis the equation following may be considered as a basis for estimating dimensions and location of a radially tapered passage:

wherein the symbols used are the same as those of the preceding equation.

In reduction to practice the radial locations of tapered passages of various dimensions for centrifugal compressor rotors embodying this invention will be found between those indicated by the equations and While the nominal compression ratio may be considered as W /W the actual compression ratio will be W /W modified by several factors including the following:

(1) Centrifugal force in effect at the entrance of a tapered passage.

(2) Fluid pressure drop from the fluid inlet of the compressor to the central chamber in the rotor due to flow resistance.

(3) Fluid flow resistance within the tapered passages.

(4) The effect of adiabatic compression within the tapered passages.

The included angle A of tapered passage 23 is a function of its outside radius R2 of discs 11, the dimension of W and the compression ratio indicated by W W A sharply acute angle A may be most elfective in compressing most gaseous fluids.

The thickness of annular disc determines the depth of the tapered passages 23. The maximum depth may be limited by the requirement for starting compression from balanced fluid pressures at the inlet and outlet of the tapered passages. The tapered passage depth will also be influenced by the characteristics of the fluid to be compressed which influence its flow, such as fluid density, viscosity, temperature, inlet pressure, etc., and the mechanical characteristics of the compressor such as rotor diameter and r.p.m. Another factor influenced by the depth of tapered passages is the amplitude of variation in the volume of the fluid which may be compressed in a unit of time, at approximately the full compression ratio of the compressor.

In operation the fluid to be compressed enters the compressor housing 1 at fluid inlet opening 20, leading into shaft seal chamber 19. From seal chamber 19 it enters hollow shaft 4 through openings 21, flows through the hollow shaft and out shaft openings 22 into the rotor central chamber 14. It then flows between the inner portion of annular disc 10, and into inlet openings 25 of the radial tapered open passages 23 in discs 10, and between discs 11. As the fluid flows radially outward through tapered passages 23, centrifugal force increases its radial pressure on the fluid progressively and substantially in proportion to the centrifugal force in effect on the fluid being compressed as it flows radially outward through passage 23. The cross section area of tapered passages 23 progressively decreases substantially in inverse proportion to the cube of the radius from the center of the rotor. Thus the radial pressure on the flowing fluid induced by centrifugal force is progressively counterbalanced by a substantially equal resistance encountered in the progressively receding cross section. area of the tapered passages 23. The receding cross section areas convert radially increasing centrifugal force into increased fluid pressure while maintaining a substantially constant flow rate of the fluid radially outward through passages 23. From the outward ends 26 of passages 23, the fluid flows between discs 10 into the compression chamber 2, from which it leaves the compressor housing 1 through the discharge opening 32.

Lubrication of bearing 5 is accomplished in operation by the pressure difference between lubricant reservoir 27, receiving high pressure from compressor housing 1 through conduits and 31, and seal chamber 1-9 subjected to intake pressure through compressor intake opening 20. Lubricant is forced up conduit 28 through drilled passages 29 to lubricate the bearing 5, from which it flows into seal chamber 19, then into shaft openings 21 through the drilled center of shaft 4, next through shaft openings 22, into the central chamber 14 of the rotor from which it is carried by centrifugal force and the flow of fluid being compressed, into compression chamber 2. A lubricant barrier 55 restrains the circular flow of lubricant around the inside circumference of housing 1 under the influence of the rotating flow of fluid leaving the periphery of the rotor, to assist its return flow through conduit 30 into lubricant reservoir 27. This completes the lubricant flow cycle.

FIG. 5 shows a vertical sectional view of a hermetic type centrifugal compressor having a housing comprising an intake chamber defined by upper housing 36, and motor casting 37, and a lower pressure chamber 38, defined by lower housing 39 and motor casting 37. Motor casting 37 provides a transverse circular partition between upper chamber 35, and lower chamber 38, and includes a central bearing 40, and an annular flange 41, holding motor stator 42. Bolts 3 and gaskets 33 hold housings 36 and 39 in assembly with casting 37.

Motor rotor 43 is mounted on the upper end of tubular shaft 44, which is journaled in bearing 40, and the assembly of the two is supported on thrust bearing 45. Tubular shaft 44 has a fluid intake opening 46 at its upper end and is closed with a plug 47 at its lower end which extends into pressure chamber 38. A compressor rotor similar to that of FIG. 1 is mounted on the lower portion of shaft 44, in pressure chamber 38. It comprises a plurality of annular discs 10 and 11, held concentrically between rotor and plates 12 by bolts 13. The hub 34 of each rotor end plate 12, fits shaft 44, and the fit is made fluid tight by an O ring 15 in each hub. The assembled rotor is secured to shaft 44 by means of shaft nut 16 exerting pressure through the rotor assembly to split retaining washer 17. Tubular shaft 44 has drilled openings 48 to provide communication between its hollow center and the rotor central chamber 14.

A supply of lubricant is held at the base of housing 39. A lubricant conduit 49, connecting to fitting 50, and drilled passages 51, provides a passage for lubricant from the base of housing 39 to the lower part of bearing 40. Hole 52 is drilled in shaft 44 at the upper part of bearing 44 to permit lubricant from bearing 40 to enter into the hollow center of shaft 44.

In operation the fluid to be compressed enters upper housing 36 at its intake opening 53, leading into intake chamber 35, from it enters tubular shaft 44 at its open end 46, and flows down the shaft and out openings 48, into the rotor central chamber 14. The fluid to be compressed then flows through tapered passages 23, formed by discs 10 and 11, in the same manner as described in the centrifugal compressor shown in FIG. 1.

The compressed fluid leaves the periphery of discs 10, to enter pressure chamber 38, from which it is discharged from the compressor through discharge opening 54.

Lubrication of bearing 40 is accomplished in operation by means of the pressure difference between pressure chamber 38, and intake chamber 35. A reservoir of lubricant is maintained at the base of housing 39, from which lubricant is pressure fed to hearing 40, through conduit 49, fitting 50, and drilled passages 51. Lubricant flowing up bearing 40 flows from the top part of bearing 40 into the inside of tubular shaft 44 where it is carried by the flow of fluid being compressed into and through the rotor and into the pressure chamber 38, wherein it flows by gravity to the lubricant reservoir at the base of housing 39. This completes the lubricant flow cycle.

It will be readily understood by those familiar with the art that two or more compressor rotors comprising this invention may be assembled to rotate on a common shaft with suitable pressure sealing means between them, and interconnected in axial series to effect a series of successive pressure stages in the conventional manner to effect a high overall compression ratio.

While specific embodiments of the present invention have been shown and described, it is to be understood that the invention is not limited thereto but is susceptible to various changes and modifications without departing from the spirit or essential attributes thereof, and I desire therefore that only such limitations :be placed thereon as are specifically set forth in the appended claims.

What is claimed is:

1. A centrifugal compressor rotor including an axial tubular shaft and comprising a stack of concentric annular discs including a number of large discs and a number of smaller discs, and end plates defining a central rotor chamber, one of each smaller discs being disposed alternately betwen adjacent large discs, said large annular discs each having a number of radial tapered slots between its inside and outside circumferences, said slots diminishing in width toward the periphery of the rotor, said smaller annular discs being dimensioned to cover said tapered slots except for their ends whereby said slots become radially tapered passages providing communication between the inside and outside circumferences of said smaller discs.

2. A centrifugal compressor rotor as set forth in claim 1 and including passage means for gaseous fluid flow through said tubular shaft into said central rotor chamber and through said radial tapered passages to the periphery of the rotor.

3. A centrifugal fluid compressor comprising a housing for receiving and discharging compressed fluid, fluid inlet and outlet openings in said housing, a shaft opening in said housing, a shaft seal means at said shaft opening, a shaft bearing within said housing, a rotor, a central chamber in said rotor, a hollow shaft for said rotor journaled in said bearing and extending through said housing opening and shaft seal means to provide means by which said rotor may be rotated, said rotor including a number of tapered passages circularly disposed and having their cross section areas diminishing outward toward the periphery of the rotor providing communication between said central chamber and the periphery of said rotor, passage and port means for fluid to be compressed to enter said housing intake opening, to flow through said hollow shaft, said central rotor chamber, said radial tapered passages into said compressor housing, and out said housing outlet passage; lubricant reservoir means associated with said housing and subjected to discharge fluid pressure therein, and passage and port means for lubricant to flow, under the pressure difference between the pressure of the incoming fluid to be compressed and the compressed fluid in said compressor housing, in a circuit from said lubricant reservoir means to said bearing, and from said bearing into said hollow shaft from which it will be propelled by the intake flow of gaseous fluid through said central rotor chamber and said radial tapered passages into said housing from which it is returned by the influence of gravity and fluid pressure difference to said lubricant reservoir means.

4. A centrifugal compressor of the hermetic type comprising a housing, a partition Within said housing dividing it into a compression chamber and a motor chamber, a fluid inlet opening in said motor chamber, a fluid outlet opening in said compression chamber, a shaft hearing as sociated with said housing partition extending between said motor chamber and said compression chamber, a compressing rotor in said compression chamber, a central chamber in said compressing rotor, an electric motor stator and motor rotor for driving said compressing rotor in said motor chamber, a tubular shaft journaled in said bearing and extending into said motor chamber and into said compression chamber with its end therein closed, said Compressing rotor being secured to the shaft extension in said compression chamber and said motor rotor being secured to the shaft extension into said motor chamber, said compressing rotor including a number of tapered passages circularly disposed and having their cross section areas diminishing outward toward the periphery of the rotor providing communication between said central chamber and the periphery of said compressing rotor, passage and port means for fluid to be compressed to enter said fluid inlet opening, to flow into and through said tubular shaft, said central compressing rotor chamber, said tapered passages into said compression chamber, and out of said compression chamber outlet opening; lubricant reservoir means associated with said compression chamber and subjected to the fluid discharge pressure therein, and passage and port means for lubricant to flow, under the pressure difference between the intake pressure within said tubular shaft and said compression chamber, in a circuit from said lubricant reservoir means to said bearing and from said bearing into said tubular shaft from which it will be propelled by the intake flow of gaseous fluid through said central compressing rotor chamber and said tapered passages into said compression chamber from which it is returned by the influence of gravity and fluid pressure difference to said reservoir means.

References Cited by the Examiner UNITED STATES PATENTS 1,013,248 1/1912 Wilkinson 10384 2,234,469 3/1941 Dick 230206 X 2,509,376 5/1950 Trask 230127 LAURENCE V. EFNER, Primary Examiner.

ROBERT M. WALKER, Examiner. 

1. A CENTRIFUGAL COMPRESSOR ROTOR INCLUDING AN AXIAL TUBULAR SHAFT AND COMPRISING A STACK OF CONCENTRIC ANNULAR DISCS INCLUDING A NUMBER OF LARGE DISCS AND A NUMBER OF SMALLER DISCS, AND END PLATES DEFINING A CENTRAL ROTOR CHAMBER, ONE OF EACH SMALLER DISCS BEING DISPOSED ALTERNATELY BETWEEN ADJACENT LARGE DISCS, BEING DISPOSED ALTEREACH HAVING A NUMBER OF RADIAL TAPERED SLOTS BETWEEN ITS INSIDE AND OUTSIDE CIRCUMFERENCES, SAID SLOTS DIMINISHING IN WIDTH TOWARD THE PERIPHERY OF THE ROTOR, SAID SMALLER ANNULAR DISCS BEING DIMENSIONED TO COVER SAID TAPERED SLOTS EXCEPT FOR THEIR ENDS WHEREBY SAID SLOTS BECOME READIALLY TAPERED PASSAGES PROVIDING COMMUNICATION BETWEEN THE INSIDE AND OUTSIDE CIRCUMFERENCES OF SAID SMALLER DISCS. 